U.S. patent number 4,263,680 [Application Number 06/021,962] was granted by the patent office on 1981-04-28 for prosthetic closure devices to replace the valves in human hearts.
This patent grant is currently assigned to Beiersdorf, AG. Invention is credited to Ernst-Wilhelm Muller, Helmut Reul.
United States Patent |
4,263,680 |
Reul , et al. |
April 28, 1981 |
Prosthetic closure devices to replace the valves in human
hearts
Abstract
A prosthetic closure device to replace a human heart valve, in
particular the mitral or tricuspid valve, comprises an annular
valve body, around the periphery of which a suture ring is provided
for attaching the valve body to the heart tissue, and a valve
member located in the valve body. The valve member is in the form
of a spherical segment having a diameter of 1.058 D.sub.ri and
comprising part of the surface of a hollow sphere having a diameter
of 2D.sub.ri, where D.sub.ri is the smallest inner diameter of the
valve body. The valve member is hinged to the valve body by means
of a flap formed integrally with the valve member and which
projects through a slot in the valve body, where it is secured by
the suture ring, to form a hinge. The inner surface of the valve
body narrows conically in the direction of inflow and subsequently
widens to provide an annular seating for the valve member.
Inventors: |
Reul; Helmut (Duren,
DE), Muller; Ernst-Wilhelm (Bornheim-Merten,
DE) |
Assignee: |
Beiersdorf, AG (Hamburg,
DE)
|
Family
ID: |
6036764 |
Appl.
No.: |
06/021,962 |
Filed: |
March 19, 1979 |
Foreign Application Priority Data
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Apr 12, 1978 [DE] |
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2815756 |
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Current U.S.
Class: |
623/2.2;
137/527 |
Current CPC
Class: |
A61F
2/2403 (20130101); Y10T 137/7898 (20150401) |
Current International
Class: |
A61F
2/24 (20060101); A61F 001/22 () |
Field of
Search: |
;3/1.5
;137/527,527.8 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2212551 |
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Oct 1972 |
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DE |
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2313271 |
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Sep 1973 |
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DE |
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Other References
Seidel, et al. "Herzklappenprothesen", Deutsche Medizinische
Wochenzeitschrift, 88Jg. No. 15, 12 Apr., 1963, pp.
748-754..
|
Primary Examiner: Crowder; Clifford D.
Attorney, Agent or Firm: Andrus, Sceales, Starke &
Sawall
Claims
We claim:
1. A prosthetic heart valve for controlling the flow of blood, said
valve comprising:
a ring-like valve body through which the blood flows; and
a dome-like valve member in said body, said valve member being
formed as a segment of a hollow sphere and presenting a convex
surface to the blood in its normal direction of flow through the
valve,
said valve member being connected to the said valve ring by a hinge
for pivotal movement between an open position permitting blood flow
through said body and a closed position in which said member rests
on a generally annular supporting surface in the interior of said
valve body to block blood flow, said hinge including a flexible
flap affixed to a portion of the periphery of said valve member,
said flap extending through a slot in said valve body and being
secured to the exterior thereof.
2. A heart valve according to claim 1 wherein said valve member is
truncated and said valve body is flattened in the region of said
hinge.
3. The heart valve according to claim 2 wherein said hinge has a
length within a range of 0.4 D.sub.ri to 0.5 D.sub.ri, wherein
D.sub.ri is the smallest inner diameter of said valve body.
4. The heart valve according to claim 1 wherein said valve member
generally represents that part of the surface of a hollow sphere
having a diameter D.sub.sph =2 D.sub.ri which is intersected by a
circle of the diameter D.sub.disc =1.058 D.sub.ri, wherein D.sub.ri
is the smallest inner diameter of said valve body.
5. The heart valve according to claim 1 wherein the thickness of
said valve member is less than 0.4 mm.
6. The heart valve according to claim 1 wherein said valve member
comprises a metal sheet coated on both sides with a
blood-compatible synthetic material.
7. The heart valve according to claim 6 wherein said flexible flap
is integrally formed with said valve member and consists of the
same blood-compatible synthetic material as that by which the metal
substrate is coated.
8. The heart valve according to claim 6 wherein said valve member
has a layer of epoxy compound intermediate said metal sheet and
blood-compatible synthetic material.
9. The heart valve according to claim 6 wherein said metal sheet
has a plurality of apertures through which the layers of synthetic
material on both sides of said sheet are interconnected.
10. The heart valve according to claim 1 further including a suture
ring on the exterior of said valve body for attaching the valve
body to the tissue of the heart.
11. The heart valve according to claim 10 wherein said valve body
has a channel-like recess on its exterior for receiving the suture
ring.
12. The heart valve according to claim 1 wherein the interior of
said valve ring initially converges in the direction of blood flow
and subsequently diverges to provide said annular supporting
surface for said valve member.
13. The heart valve according to claim 12 wherein said slot for
said flap is located in the diverging portion of the interior of
said valve ring.
14. The heart valve according to claim 6 wherein said valve body is
formed of metal and is coated with the same blood-compatible
synthetic material as said valve member.
Description
BACKGROUND OF THE INVENTION
This invention relates to prosthetic closure devices to replace the
valves in human hearts, in particular the mitral and tricuspid
valves, having a valve body in the form of a ring, a suture ring
for attaching the valve body to the tissue and a valve member
positioned in the valve body.
The history of artificial heart valves already covers a period of
over twenty-five years and began with the first valve implanted by
Hufnagel in 1952. Since then the problems of developing and
perfecting artificial heart valves have not been completely solved,
which results in the large number of around forty types of valves
in use today.
At present spherical and disc valves are the leaders in the field,
and also in the last few years replacement valves for special uses
made from pig's heart valves have also gained in importance.
However, the results obtained with all closure devices of this type
are not satisfactory. For example, the average survival rate of
patients with an artificial heart valve is still under five
years.
The resultant complications can essentially be reduced to four
reasons:
flow mechanics reasons,
mechanical reasons,
biological reasons,
material reasons,
or combinations of these four.
Mechanical reasons for a valve defect can be material fatigue,
breakage or deformation of a valve either due to mechanical stress
or chemical corrosion. Amongst defects of a biological nature,
inflammation and rejection of the material which is foreign to the
body are frequently encountered. Defects due to flow mechanics,
such as destruction of red corpuscles in areas of high localised
shear stress and the formation of thromboses in areas of low speed
of flow, are further important reasons. Shear stress and
distribution of speed with the above-mentioned characteristics are
to be found in all valves, since they restrict the blood flow in
various ways:
(a) by the valve member itself, which forces the blood to flow
through an annular slot between the valve member and the valve body
(with spherical or disc valves) or in two separate flow channels
with a different form of flow separation (with centrally placed
disc valves);
(b) by the valve member mounting support (cages, clamps); and
(c) by the complete valve body, which consists of valve seating and
suture ring.
Contrary to the properties of existing artificial heart valves,
natural valves permit a central, undisturbed flow with a smooth
opening and closing action and without any back flow. A further
great disadvantage of most artificial heart valves is the
psychological stress suffered by patients during the noise of
opening and closing.
It can therefore be summarised that the currently used types of
valves do not satisfactorily comply with functional requirements.
The reasons for defects in known valves can be summarised as
follows:
(a) Pressure gradients, which cause increased pumping work, loss of
efficiency and insufficient inflation of the heart chamber;
(b) high localised shear stress which causes damage or destruction
of the cellular blood components;
(c) back flow on closing of the valve of the order of 5% to 10%,
and
(d) formation of thromboses in areas of low speed of flow.
The invention is based on the problem of producing a closure device
suitable for replacing the valves in human hearts, and especially
suitable for the mitral and tricuspid valves, with which the
disadvantages previously pointed out can be overcome and in
particular a smooth, undisturbed flow both in the open and closed
positions can be achieved and "dead water" zones causing thromboses
and also high shear stress which is harmful to the blood can be
avoided.
SUMMARY OF THE INVENTION
According to the invention there is provided a prosthetic closure
device to replace the valves in human hearts, in particular the
mitral and tricuspid valves, having a valve body in the form of a
ring, a suture ring for attaching the valve body to the tissue and
a valve member positioned in the valve body, wherein the valve
member is in the form of a spherical segment having a diameter of
substantially 1.058 D.sub.ri and generally comprises part of the
surface of a hollow sphere having a diameter of substantially
2D.sub.ri, where D.sub.ri is the smallest inner diameter of the
valve body.
Contrary to the known disc valves, the valve member according to
the invention is of dish-shaped formation, that is, in the form of
a sperical segment. Being in the form of a spherical segment serves
on the one hand to increase the strength of the valve member (in
the closed position differences in pressure of up to 300 mm Hg can
occur) and on the other hand has functional reasons which are
explained below, taking the mitral valve as an example. When the
ventrical fills, the mitral valve opens very quickly. The flow of
blood entering the ventrical reaches the top of the chamber,
spreads out sideways and upwards behind the two natural valve flaps
and produces at the same time a strong ring vortex in the expanding
ventrical, which holds the two flaps in a stable position. When the
inflow slows down, the pressure difference on both sides of the
flaps causes a movement towards the closed position. Thereby the
mitral valve is already closed before the contraction of the
ventrical and therewith the outflow phase begins.
These functional relationships lead to the conclusion that only a
heart valve having a closure element of approximately the same form
and dimensional position as the large flap of the mitral valve is
in a position to make this above-mentioned physiological dynamic
flow phenomenon effective. This apsect is taken into account in the
construction according to the invention. It has been shown that the
vortex produced behind the dish causes the valve to close before
the start of the ventrical contraction. The diameter of the
spherical segment is of the order of the size of the vortex
diameter, whereby the dish adapts harmoniously to the
above-mentioned physiological flow path.
With the solution according to the invention, anatomical,
physiological and biochemical criteria are taken into
consideration. The construction guarantees in particular a smooth,
undisturbed flow both in the open and also in the closed positions,
and thereby avoids "dead water" zones leading to thromboses and
high shear stresses which are harmful to the blood. Moreover, the
closure device according to the invention permits a central flow
without any obstruction in the bloodstream, simulates the
physiological flow inside the heart chambers, uses the accompanying
flow power during the closing process, thereby reducing or
eliminating the back flow, closes absolutely tight and works
noiselessly.
The closure device according to the invention fulfils the following
requirements:
(a) undisturbed flow in the open position, since the dish is wide
open and substantially parallel to the inflow direction;
(b) minimal flow resistance and good conduction of the blood to the
outflow tract in the closed position, since the dish is then fully
embedded in the valve ring and lies parallel to the valve
surface;
(c) low shear stress on account of the large opening surface and
avoidance of obstructions to flow in the bloodstream;
(d) no "dead water" zones, since there are no flow
obstructions;
(e) production and use of the chamber vortex to support the end of
the valve; and
(f) completely tight closure.
The closure element according to the invention works in the
following way:
When the pressure on the convex side of the valve exceeds the
pressure on the concave side, the valve opens wide. The opening
angle .alpha. is therefore determined by the amount of blood
flowing in and the pressure difference available. Once the opening
angle has reached about 45.degree., the area between the edge of
the valve member and the valve body, which defines the free flow
cross-section at smaller opening angles, corresponds to the
cross-sectional area of the opening in the valve body. The blood
then flows completely unobstructed by any elements through the
opening cross-section and forms a vortex behind the dish in the
concave area.
The thickness s of the valve member preferably amounts to less than
0.3-0.4 mm. This has the advantage that, compared to traditional
valves, very short opening and closing times can be achieved, since
the moment of inertia of the thin dish is very small in comparison
with spherical or disc valves. This fact guarantees that the valve
can react almost instantaneously to the quickly changing pressure
gradients inside the heart chamber and thus resembles the natural
valve more closely than any other existing artificial heart
valve.
Furthermore the valve member is preferably connected to the valve
ring by a hinge and is truncated in the area of the hinge. In
contrast to the known spherical or disc valves, no flow
obstructions in the flow path occur during the inflow phase,
whereas these are unavoidable with traditional types of valves
because of the presence of cages, clips etc. The appropriate length
of the hinge area should be k=0.4-0.5 D.sub.ri.
With regard to the special formation of the hinge, the valve is
pivoted on the valve ring preferably by means of a small flat flap
which enters the area k through a slot in the valve ring and is
fastened with this on the outer side of the valve ring.
The advantages relating to the removal of any flow obstructions in
the flow path are especially in evidence in a preferred
construction in which the inner surface of the valve ring narrows
conically in the direction of inflow and subsequently widens in
such a way that a substantially annular seating for the valve
member is formed. In this form the valve member is pivoted on the
valve ring at the end area of the contact surface.
The form of the device described above is also especially
advantageous with regard to a tight closing of the valve. When the
pressure difference reverses above the valve, there results a quick
closure, and the dish is supported on the seating and is at the
same time centralised. The inflow region in the valve ring itself
is of slightly conical shape (10.degree.-15.degree.) to obtain a
better flow.
The valve ring is preferably provided on its outer side with a
channel-like recess for holding the suture ring. The shape of the
suture ring depends on the area of implantation in the heart and is
not a subject of the invention. The suture ring consists, as is
usually the case, of knitted or woven polyester material.
With regard to the material for the valve member, this
advantageously comprises metal coated on both sides with
blood-compatible synthetic material. Naturally other suitable
materials, such as synthetic, ceramic or similar materials can be
used instead of metal. The metallic valve is in particular coated
with the blood-compatible material by a dipping process. In order
to guarantee good contact of the synthetic material with the metal,
before coating the valve member with the blood-compatible synthetic
material it is first coated with a 1 .mu.m thick layer of a special
epoxy compound. Therefore with this special form of the device the
valve member comprises a metal substrate with a first layer about 1
.mu.m thick of an epoxy compound and a second layer of
blood-compatible synthetic material. In order to further improve
the adhesion of the synthetic material to the metal, the metal
substrate is preferably provided with a number of apertures
arranged in concentric circles, by means of which connection
between the layers of synthetic material on both sides is produced.
The hinge flap is advantageously formed in one piece with the valve
member and consists of the same blood-compatible synthetic material
with which the valve member is coated. It is preferably integrally
cast in the course of the above-mentioned coating process, so that
it is connected with the valve member without transition.
The valve ring advantageously consists of metal and is coated with
the same blood-compatible synthetic material as the valve member.
In this case also, synthetic, ceramic or similar materials can be
used instead of metal.
Thereby three advantages are obtained at the same time:
(a) the direct contact of synthetic material to metal between the
valve member and valve ring is avoided (low amount of
friction),
(b) the sealing effect is improved with the smooth synthetic
material, and
(c) development of noise is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an underneath plan view of a prosthetic closure device in
accordance with the invention,
FIG. 2 is a cross-sectional view of the device taken along the line
II--II of FIG. 1, and
FIG. 3 is a detailed, partial cross sectional view taken along the
line III--III of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in FIG. 1, the closure device comprises a valve body 2 in
the form of a ring, a suture ring 3 fixed around the circumference
of the valve body 2 and which serves to hold the closure device in
the tissue, and a valve member 1 located in the valve body 2. The
valve member 1 is in the form of a dish having a diameter
D.sub.disc =1.058 D.sub.ri and generally comprises part of the
surface of a hollow sphere having a diameter D.sub.sph =2 D.sub.ri,
where D.sub.ri is the smallest inner diameter of the valve ring 2.
The valve member 1 is connected to the valve ring 2 by a hinge 4
and is truncated in the region of the hinge 4 to form a straight
edge. The hinge 4 has a length k=0.4-0.5 D.sub.ri.
In FIG. 2 the closure device is shown in cross-section along the
line II--II of FIG. 1. The open position of the valve member 1 is
indicated by dotted lines. It can be seen that the valve ring 2 is
formed in such a way that its inner surface 6 narrows conically in
the direction of flow and subsequently widens so that an annular
valve seating 9 (D.sub.disc -D.sub.ri) for the valve member 1 is
formed. In the area of the hinge 4 the valve member 1 is provided
with a small flap of synthetic material 7 serving as a hinge and
extending beyond the edge of the valve member 1. By means of this
flap of synthetic material 7 the valve member 1 is hinged to the
valve ring 2 in the region of the valve seating 9, as shown at the
left-hand side of FIG. 2. The valve ring 2 is provided with a slot
8 in the region of the hinge 4, which extends through the valve
ring 2. The flap of synthetic material 7 is drawn through this slot
8 and is fastened on the outer side of the valve ring in a
channel-like recess 10 which is provided to hold the suture ring 3.
Thereby the flap of synthetic material 7 is held in position
between the valve ring 2 and the suture ring 3. In this way an
efficient attachment of the valve member 1 to the valve ring 2 is
ensured, without any obstructions to the flow occurring in the flow
path.
The valve member 1 illustrated in the drawings comprises a metallic
material 12, which is coated on both sides with a blood-compatible
synthetic material 14. In order to obtain better adhesion of the
layer of blood-compatible synthetic material 14 to the metal
substrate 12, the metal substrate is coated with a layer 16
approximately 1 .mu.m thick of an epoxy compound and furthermore is
provided with a number of apertures 5 arranged in concentric
circles, which enable the layers of synthetic material on each side
of the metal substrate to be interconnected. In the finished valve
member these apertures are completely filled with synthetic
material 14.
The closure device described above was submitted to the following
test, together with a Bjork-Shiley disc valve, one of the most
widely known artificial valves:
(1) Measurements in pulsating, physiological flow in a
closed-circuit simulator (pulse volume 80 cm.sup.3, pulse frequency
70/min, mitral position).
______________________________________ Closure device according to
the Bjork-Shiley invention disc valve (D.sub.ri = 27 mm) (D.sub.ri
= 27 mm) ______________________________________ Peak opening
pressure (mmHg) 10.1 21.1 Average pressure difference during
opening phase (mmHg) 0.75 2.45 Average energy loss during opening
phase (joules) 0.8 .times. 10.sup.-2 2.6 .times. 10.sup.-2 Back
flow due to leakages 0% 10%
______________________________________
The closure device according to the invention was moreover
submitted to a fatigue test, with a stress cycle frequency of
700/min and a pressure difference of 130 mmHg, which commenced on
the Nov. 22, 1977. This test produced about 1 million stress cycles
per day.
The number of stress cycles completed up to the Mar. 3, 1978 was 98
million, which corresponds to a life span of 2.6 years with normal
frequency of 70/min. Up until that date no appearance of fatigue
had been observed at all. The life span aimed at is 10 years (367
million stress cycles) at normal frequency.
The results given above show that the closure device according to
the invention possesses essentially better properties than the disc
valve which has been most widely known.
* * * * *